Revolving doors and, more particularly, revolving doors adapted to be collapsed in certain situations are well-known.
The U.S. Pat. No. 3,495,251 to Lowe (issued Feb. 10, 1970) discloses a collapsible revolving door wherein there are top and bottom cam housings, each having a central cam. The mechanism includes four cam followers (one for each door) held in position by spring biased ball detent mechanisms. Pins extend from ends of the cam followers adjacent the cam through radial slots in the cam housing. The ball in each detent mechanism presses against a ball socket in the circumferential wall of the central cam housing. Extraordinary force applied to the doorwings causes the ball in the detent mechanism to ride up out of the ball socket on the central cam housing and allows the doorwing to rotate about the axis of the pin extending from the end of the cam follower. The translational motion of the doorwing is guided by the pins which extend through radial slots. In a fully collapsed position, all four wings are parallel.
The Rush U.S. Pat. No. 3,736,701 (issued June 5, 1973) discloses a revolving door having a collapsing mechanism similar to that disclosed in the Lowe '251 Patent. In Rush, the upper and lower mechanisms are without a load bearing or torque transmitting central shaft. These mechanisms are coupled to the roof and floor of the doorway.
In the Lowe and Rush systems, the force at which the doors collapse is not easily adjustable. The mechanisms must be completely disassembled and new hardware provided in order to change the collapsing force.
The U.S. Pat. No. 2,111,182 to Hagenbook (issued Mar. 15, 1938) discloses a revolving door mechanism wherein radially positioned spring-biased reciprocatory plungers in central hubs engage rollers in each doorwing to maintain the wings in radial position. As pressure is applied to the door, the reciprocatory plunger retracts as it slides up over the roller to allow the wings to collapse. The spring force on the plungers appears to be adjustable through set screws but it appears that adjustment would require disassembly of the hardware.
The above-described revolving door mechanisms, do not provide for easy adjustment of the force at which the collapsing mechanisms collapse the doors. The top collapsing mechanism may be required in different environment to collapse the doors at different force levels.